1. Field of the Invention
The present invention relates to a polishing/grinding apparatus capable of providing high surface precision, and more particularly to a polishing/grinding apparatus in which the polishing operation is achieved by pressing a running polishing tape as the polishing material against the surface to be polished.
2. Related Background Art
(1) Optical parts, such as the lens for use in a camera, have spherical and aspherical surfaces and require a highly precise surface coarseness, and also require high dimensional precision with respect to the design values of spherical and aspherical surfaces.
Manufacturing precision can be relatively easy to achieve if the amount of asphericity is small, but, when it becomes large, it is extremely difficult to maintain the desired precision.
When a glass material is given a certain surface coarseness by a preliminary working and certain tool and polishing conditions (polishing material, polishing pressure, polishing speed etc.) are selected, it is known that the amount of abrasion in this system is proportional to the polishing time, and this principle is utilized in the control of work piece and tool in so-called computer controlled polishing. Among such apparatus for computer control of the work piece and tool:
Apparatus in which an aspherical work piece is rotated are disclosed in the U.S. Pat. Nos. 3,566,544, 3,564,776 and 3,769,762;
Apparatus in which a work piece is rotated while a tool is moved in the radial direction are disclosed in the U.S. Pat. Nos. 3,566,544 and 3,564,776; and
Apparatus in which a work piece is fixed while a tool scans in the X- and Y-directions are disclosed in the U.S. Pat. Nos. 3,587,195, 3,589,078 and 3,676,960.
(2) The present invention relates to an apparatus for achieving a polishing operation by pressing a polishing tape, supplied from a supply side against a takeup side, to the surface of a work piece to be polished. A prior art device utilizing the polishing tape is disclosed in the Japanese Laid-open Patent 181561/83, which describes a polishing apparatus comprising a shaft capable of supporting a magnetic disk; a pad roller covering with an elastic member a main surface positioned at a side of the magnetic disk supported by said shaft; a polishing tape maintained in contact with said pad roller and rendered movable; and an air bearing positioned corresponding to said pad roller across said magnetic disk and having a rotating portion with an external tube of truncated conical shape; wherein the axis of the rotating portion of said air bearing is so positioned as to substantially cross the rotating portion of said shaft, and said magnetic disk is pinched by said pad roller and the rotating portion of said air bearing, thus maintaining said polishing tape in contact with the magnetic disk rotated by said shaft and thereby polishing the surface of said magnetic disk.